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Comment by function_seven | Hacker News Reader

> It's a perpetual energy source right in front of us

It's not. Once something has fallen down, it can't fall down again.

To draw energy from the gravitational attraction of 2 bodies, you must first separate them. That consumes energy.

On second thought, I suppose tidal energy fills the bill. Extracting that energy is really exploiting the Moon's motion, using gravity as the "conduit". Not strictly perpetual, but essentially so for our needs.

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Isn’t tidal energy just harnessing some of the existing gravitational potential energy of the Moon-Earth system, which is roughly similar to any system that harnesses energy from a massive object falling due to gravity?

But again, slowing tidal currents must be drawing energy from somewhere until there is none left.

It basically draws energy from the moon orbiting earth. It could theoretically alter that orbit, but given that the moon/earth system has a lot of mass, the timescale for that to happen is extraordinarily large.

That’s exactly what it’s doing. It’s slowing down Earth’s rotation and speeding up the Moon’s orbit (i.e. moving the Moon further from the Earth).

But that "something" keeps being pulled down until it is stopped/blocked by something (e.g. the ground). Gravity is perpetual relative to the source of the gravity. It's just that our surroundings change and give the illusion of gravity changing...i.e. we don't "run low" on gravity

I don't think Maxwell's Demon is 100% solved.

Tidal energy could play into it, some underwater tides deep in the ocean are insanely strong.

You're confusing force with work. Gravity is a perpetual force, but a force doesn't generate energy.

To generate power you need gravity to move something downwards, releasing the potential energy. And when that thing hits the bottom of the shaft you've used up all the potential every that was stored in it.

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